Laminography techniques are widely used to produce cross-sectional images of selected planes within objects. Conventional laminography requires coordinated motion of any two of three main components comprising a laminography system (i.e., a radiation source, an object being inspected, and a detector). The coordinated motion of the two components can be in any of a variety of patterns, including linear, circular, elliptical and random patterns. Regardless of the pattern of coordinated motion selected, the configuration of the source, object and detector should ensure that, during a cycle of the pattern of motion, any given point in the object plane (i.e., the plane of focus within the object) will always be projected onto the same point in the image plane (i.e., the plane of the detector), and that any point outside the object plane will be projected to a plurality of points in the image plane.
In laminography, it is important to keep the focal plane very thin. If the coordinated motion is as it should be, a sharp cross-sectional image of the plane within the object that is in focus will be formed on the detector. Cross-sections of the object that are not in the focal plane (i.e., background images) will be blurred on the detector. The result is a sharp image of the desired plane within the object. In a laminography system that has a field of view that is smaller than the object being inspected, it may be necessary to move the object around within the field of view (FOV) of the laminography system to obtain multiple laminographs which, when pieced together, cover the entire object. Movement of the object is frequently achieved by supporting the object on a mechanical handling system, such as an X, Y, Z positioning table, that can be moved in the X, Y and Z directions. The table is moved to bring the desired X, Y regions of the object into the field of view (FOV) of the laminography system. Once the X, Y region of the object to be imaged is within the FOV, the object is moved in the Z directions so that the planes within the object where the cross-sectional image is to be obtained are generally parallel to the focal plane of the laminography system. Once the desired planes within the object along the Z-axis have been imaged for a given X, Y region, the X, Y, Z positioning table moves the object so that the next X, Y region to be imaged is within the FOV of the laminography system. The desired planes within the object along the Z-axis are then imaged by moving the object to selected positions along the Z-axis. This process continues until all of the desired cross-sectional images, or slices, needed to inspect the object have been obtained.
While this method of moving the object in the X, Y and Z directions to perform laminography enables various areas and planes of the object to be imaged and analyzed, there are limitations associated with the speed and accuracy of existing mechanical positioning systems. These constraints effectively act to increase cycle time, thereby reducing the rates at which inspection can occur. Furthermore, with existing mechanical positioning systems, the mechanical motions produce vibrations that tend to reduce the system resolution and accuracy. In addition, the laminographs obtained by such systems may be imprecise.
Accordingly, a need exists for a laminography positioning system that improves the accuracy of the laminographs and that enables laminographic inspection to be performed with great precision and improved throughput.